Hi NinaK8
This is not strange - this is MYOB! AR2023 had always had dozens of bugs in the Inventory module. Over the years they have fixed some, and then seemingly given up on fixing the rest. There have been numerous forum posts about COGS on P&L in the trillions, billions etc.
Trying to edit and fix individual transactions often only makes things worse. I would advise against this.
Generate an Inventory Value Reconciliation report and see what the current negative value is. If this shows for example 50 on hand and -$2b, and the true cost of each pallet is $2, do an Inventory Adjustment Journal to adjust the on hand by 0 and the value by +$2b +100 or +2,000,000,0100, this should adjust the value for this item back to $100. Use the COGS account as the balancing account.
Then speak to your accountant about the best way to adjust the P&L and Balance sheet to correct any of MYOB's 'anomalies'.
Regards
Gavin